The present invention relates to a method for applying a thread onto a relatively moving substrate. The present invention also relates to devices for carrying out the method.
Such a method and device for applying a thread onto a relatively moving substrate is described in Swedish Patent No. 209 771. It describes how lengths of thread can be laid substantially transversely over longitudinal threads moving thereunder to thereby form a net elastic web. Two wheels inclined towards each other above the substrate of longitudinal threads almost touch at the top. Each of the wheels is provided on its periphery with uniformly spaced fingers which alternatingly hook a thread dispensed centrally from a spool to said point of contact between the inclined wheels, as the wheels rotate. The alternating hooks thus move away from each other as they are moved with the periphery of their respective wheels, thereby gradually extending the thread, somewhat in the manner of a xe2x80x9ccat""s cradlexe2x80x9d, in a zigzag pattern from one wheel to the other, reaching its broadest extent directly above the substrate and diametrically opposite to the pick-up point of contact between the two wheels. In the method and device shown in this Swedish patent specification, the transversely extended threads, upon reaching their point of greatest extension, are cut by a knife and glued to the longitudinal threads.
By this known method and device however with uniformly spaced fingers and where the threads are cut off in transverse lengths, only a transverse pattern can be created with the thread. In the manufacture of elastic pants products such as pants diapers cut end-to-end from a web, it is necessary to lay elastic threads transversely in the waist area for example, and longitudinally to elasticize the leg openings for example. Up to now this has involved a number of different separate process procedures making the method complex, and thus costly and/or prone to error, and different threads which have to be glued separately, at least at their ends, and this can give rise to a number of loose ends in the product.
All of these problems are solved by the method described herein. In this way it is possible to apply a single or several parallel elastic threads continuously along a pants diaper web of indefinite length, thus providing both transverse elasticity in the waist portion and sealing elasticity around one or more leg openings as well as longitudinal elasticity over the crotch portion, as will be evident from the detailed description of the present invention.
One inventive device for carrying out the method according to the invention removes certain of the projecting elements from one or both of the wheels enabling the device to lay down the thread continuously with both transverse zigzag portions and entirely longitudinal and/or inclined longitudinal portions.
A second inventive device for carrying out the method according to the invention includes projections that can be shaped so that certain of them release the thread from engagement, thus creating the same pattern as with the device described above but with a different elasticity in the longitudinal portions.
According to one particularly advantageous embodiment of the invention, the projecting elements or fingers are mounted externally on belts running on the inclined wheels, which in this case are pulleys. The belts run on the inclined pulleys from the pick-up point to the points diametrically opposite therefrom. The belts leave the front inclined pulleys there however, keeping the thread in its extended zigzag/longitudinal pattern. The thread can either be pressed by suitable means, a roller for example, off the projections into application against the substrate or the belts can be twisted inwards by virtue of a second pair of pulleys being vertically aligned or oppositely inclined to the first pair of wheels/pulleys, or the two methods can be combined. According to a preferred practical embodiment, two pairs of inclined wheels in spaced longitudinal and transverse relationship transfer the thread, preserving its zigzag/longitudinal pattern, to a conveyor belt carrying fingers or projections running in two parallel rows.
The method according to the present invention can be used with particular advantage in, but is not limited to, the manufacture of disposable absorbent articles such as diapers, pant diapers, sanitary briefs, incontinence shields etc.